Carbon monoxide is more effective agent that carbon below 983 K but above this temperature the reverse is true. How would you explain this?

In the production of iron from its oxide ore, the mixture of ore, coke and limestone is heated with a blast of air in furnace. Below 983K oxides of iron are reduced by carbon monoxide to iron.

Fe₂O₃ +CO → 2FeO +CO₂

FeO +CO → Fe + CO₂

Above 983K, Fe₂O₃ undergoes reduction by hot coke to iron. This region is called fusion zone

Fe₂O₃ +3C → 2Fe  +3CO +Heat

Thus carbon monoxide is more effective agent than carbon below 983K.